Method of increasing strength of frozen soil



Nov. 7, 1967 A. L. SHRIER 3,350,888

METHOD OF INCREASING STRENGTH OF FROZEN SOIL Filed July 20, 1965 FIGURE I FIGURE 2 A. L. SHE/ER mvernon I I 1 BY "'10 a? f PATENT ATTORNEY United States Patent 3,350,888 METHOD OF INCREASING STRENGTH F FROZEN SOIL Adam L. Shrier, Orange, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed July 20, 1965, Ser. No. 473,427

Claims. (CI. 61-36) ABSTRACTOF THE DISCLOSURE This discovery concerns a method for increasing the structural strength or" frozen soil compositions and a method of using such composition to construct an underground reservoir.

It has long been recognized that underground reservoirs can be used'for storing liquefied gases such as liquefied natural gas, liquefied propane gas, and the like. Underground reservoirs have already been proposed wherein the reservoir is lined with a material, e.g., a steel liner, that is impervious to the product stored. In addition, the walls of such reservoirs are often lined with reinforced concrete to provide structural strength to support the roof and to prevent the earth walls from crumbling into the reservoir. Such constructions are expensive and thus are undesirable.

' In some structurally strong soils, a reservoir can be excavated and thereafter be given structural strength by saturating the soil around the reservoir and freezing the saturatedsoil. The frozen, saturated soil walls of the reservoir are strong enough to support the roof of the reservoir and areimpervious to the liquefied gas contained in the reservoir. Such construction is relatively inexpen sive.

Unfortunately, this vtype of construction is not suitable for' structurally weak soils such as sand or silt. In many instances such construction is altogether unsuitable. The saturated soil construction can be used in certain instances in locations having structurally weak soil provided the reservoir is properly designed. For example, the walls of the reservoir could be slanted rather than vertical to reduce the chances of the soil walls crumbling into the reservoir ,and to obtain sufficient structural strength to support the roof. This type of construction is economically unattractive because a much larger roof is required for a reservoir of a given volume.

A method of increasing the strength of soil has now been discovered that permits vertical wall construction. The discovery is particularly applicable to structurally weak soils such as sand, silt, or the like, but also has application to stronger soils.

In accordance with the instant discovery, soil is admixed with a fibrous, inert filler in a ratio of soil to filler in a range of from about 1:20 to 100:1 by weight and preferably in a soil to filler ratio in the range of from about 1:1 to 50:1 by weight. A liquid is added to the soil-filler admixture in an amount at least sufficient to saturate the admixture. The saturated admixture is then frozen.

The materials that are admixed with soil are fibrous fillers, such as spun glass, plastic fibers, rock wool, shredded hemp, expanded mica, sawdust (wood fiber),

pact fillers in the form of beads, chunks, and fragments does not produce the desired effect. The ratio of fiber length to the diameter of the fiber should be at least 5:1 and preferably higher than 15:1. The fibers should be as long as the circumstances permit. The strength of the resulting soil composition is directly proportional to the length of the fibers. However, the fibers must not be too long or admixing of the soil and fiber will be difiicult, and/or the pumping, if necessary, of the admixture Will be difiicult or perhaps even impossible. For the applications suggested herein, the fibers should have an average length of from about /8 inch to 6 inches.

It is desirable to mix the soil and filler until a homogeneous admixture is obtained. Although homogeneity is to be sought, it may be difficult with theequipment at hand to achieve. In any event, the soil and filler should be thoroughly mixed to avoid having segregated pockets of filler or soil.

The mixing step can be performed in conventional equipment. It may be desirable to add. 1iquid,even an excess of liquid, during the mixing step. Thereafter the excess liquid can either be evaporated from the admix.

ture or it can be left in the slurry of the slurry to the construction site.

Almost any liquid is suitable for the process hereindescribed provided that it can be frozen with the refrigeration means that are available at the construction site.

to facilitate pumping Water is preferred because of its low cost and availability.

material may result from settling of the soil and filler or from segregation of the soil from filler.

Freezing the saturated soil-filler admixture yields a structurally strong material. In some instances the strength of the composition can be further increased by adding a wetting agent to the system. If the soil and/or filler are not wet by the'liquid used to saturate the composition, small air bubbles can form on the external surfaces or in the pores of the soil and/ or filler thus causing weak spots in the frozen composition. If a small amount of a wetting agent, e.g., from about 0.02 to 2.0 wt. percent, based on the weightof liquid, is added to the liquid, this problem is obviated. Conventional wetting agents are suitable. For example, if water is the liquid, suitable wetting agents include anionic agents such as sodium benzene sulfonate, short-chain C C alkyl aryl sulfonates, shoitchain dialkyl sulfosuccinates, and short-chain alkyl sulfates; and nonionic compounds such as C -C fatty acid polyglycol esters, and alkyl aryl polyglycol ethers and their derivatives can be employed. These Wetting agents are preferred, but are not the only agents that can be employed. Other agents can be used without departing from the scope of this discovery.

The composition produced by the method hereindescribed has widespread application in extremely cold areas and in areas where adequate refrigeration is readily available. It is particularly suited for forming impervious structural elements for storage reservoirs for liquefied gases. The composition is sufficiently strong to permit vertical construction of reservoirs even in those areas having structurally weak soils. In some instances, it will be desirable to utilize the method described herein to increase the strength of soil that is relatively strong as compared with sand or silt.

The composition produced by the method hereindescribed can be used as the load bearing, vertical walls in an underground reservoir. For example, in a location having sandy or silty soil, a reservoir of the desired dimensions can be excavated. Part of the soil removed during excavating is admixed with a filler, e.g., grass or other inexpensive fibrous material, and the admixture is saturated with water as described hereinabove. The walls of the reservoir are then lined with the saturated admixture. The lining should be sufiiciently thick to support both the soil adjacent the lining and the roof which oftentimes is constructed of prestressed concrete. The required thickness will vary according to the weight of the roof and the strength of the soil adjacent the lining and may vary from top to bottom, but should generally be at least /2 foot, and preferably, within the range of from 1 to 6 feet.

The lining may also be applied to the floor of the reservoir; it is usually, however, not required except to make the floor impermeable to the material stored in the reservoir. Impermeability of the floor can be achieved more easily by merely saturating the ground with water immediately prior to filling the reservoir with the liquefied gas. The water freezes and forms a barrier.

The lining can be frozen into place in a variety of ways. For example, as shown in the cross-sectional view depicted in FIGURE 1, a form, e.g., wooden, enclosing a volume equal to the volume of the desired reservoir is constructed within the excavation.

A space is left between the sides 1 and 3 of the form and the earth walls 5 and 7 for the installation of the freeze pipes 9, 10, 11, 12, 13, 14, and 15. A plurality of freeze pipes is placed around the form at sufficiently close intervals to solidly freeze the lining material that is subsequently poured into the space between the form walls and the earth walls. The freeze pipes are fed by a header 16. FIGURE 1 shows the cavity surrounding the form to be partially filled with the lining composition 17.

After the cavity surrounding the form has been filled, or as it is being filled, a refrigerant is pumped into header 16 to supply the freeze pipes. As soon as the lining composition has frozen, the form can be removed and as shown in FIGURE 2, a roof 20 constructed of prestressed concrete or other suitable material.

The reservoir is then filled with a liquefied gas through conduit 21. As soon as the reservoir is filled, the refrigerant can be removed from the freeze pipes because the liquefied gas in the reservoir will provide adequate refrigeration for the purpose of maintaining the lining in a frozen condition. When the liquefied gas is removed from the reservoir via conduit 23, refrigerant should again be pumped into the freeze pipes.

The method described herein for freezing the lining composition in place is only one of many conceivable methods. Other methods can be devised by those skilled in the art. For example, one could line the walls of the reservoir without using the wooden form or the freeze pipes by filling a pliant container, e.g., a polyethylene bag, with liquefied natural gas and surrounding the container with the lining composition.

The results of various qualitative impact tests that were performed indicated that the discovered concept described herein is effective in increasing the strength of frozen soil samples. For example, it was found that a frozen composition comprising grams of sand, 1 gram of hemp 0/2 inch shred), and 30 cubic centimeters of water was much stronger than a frozen composition consisting of sand and water in the same proportions.

The discovery and methods for utilizing the discovery have been described herein with a certain degree of particularity. Deviations can be made without departing from the basic concepts described herein.

What is claimed is:

l. A method of increasing the strength of a frozen soil composition comprising mixing soil with a fibrous filler in a ratio of soil to filler in the range of from about 100:1 to 1:20 to increase the strength of the resulting composition, adding a liquid to the soil-filler admixture in an amount at least sufficient to saturate said admixture, and freezing the saturated admixture.

2. A method according to claim 1 wherein a wetting agent is added to the com-position before freezing in an amount sulficient to ensure that the soil and filler particles are wet by the liquid.

3. A method of increasing the strength of a structurally weak soil comprising: mixing said structurally weak soil with a fibrous filler in a ratio of soil to filler in the range of from about 100:1 to 1:20, adding water to the soilfiller admixture in an amount sufficient to saturate said admixture, and freezing the saturated admixture.

4. A method of constructing a structurally strong underground reservoir comprising lining the soil walls of a cavity with a composition comprising an admixture of soil and a fibrous filler, wherein the ratio of soil to filler is in the range of about 100:1 to 1:20, and a liquid in an amount sutficient to at least saturate said admixture; and freezing the saturated admixture to form a structurally strong lining in the cavity.

5. A method of constructing a structurally strong underground reservoir in a location having sandy soil comprising: (1) lining the vertical walls of an underground cavity with a composition comprising a water saturated, substantially homogeneous admixture of sandy soil and fibrous filler, wherein the ratio of the soil to filler is in the range of about 100 to 1 to l to 20, and (2) freezing said admixture to form a structurally strong lining in the cavity.

References Cited UNITED STATES PATENTS 2,961,840 11/1960 Goldtrap 6'10.5 X 3,183,675 5/1965 Schroeder 61--36.1

DAVID J. WILLIAMOWSKY, Primary Examiner.

JACOB SHAPIRO, Examiner. 

1. A METHOD OF INCREASING THE STRENGTH OF A FROZEN SOIL COMPOSITION OMPRISING MIXING SOIL WITH A FIBROUS FILLER IN A RATIO OF SOIL TO FILLER IN THE RANGE OF FROM ABOUT 100:1 TO 1:20 TO INCREASE THE STRENGTH OF THE RESULTING 